Method of producing spark plug center electrode

ABSTRACT

A method for the production of a spark plug center electrode comprising steps of forming a good heat conducting metal piece into a convex or protrudent shape and a corrosion-resistant metal piece into a concave or cup-shaped shape, preparing an extrusion material by fitting the protruding portion of the convex-shaped good heat conducting metal piece into the recessed portion of the concave-shaped corrosion-resistant metal piece, and coldextruding and extrusion material into a rod form such that the corrosion-resistant metal covers the good heat conducting metal.

United States Patent 1191 Yamaguchi et al.

[ 1 Dec. 31, 1974 METHOD OF PRODUCING SPARK PLUG CENTER ELECTRODEInventors: Terumoto Yamaguchi, Anjo;

Kanemichi Izumi, Oobu, both of Japan Assignee: Nippondenso Co., Ltd.,Kariya-shi,

Aichi-ken, Japan Filed: Aug. 1, 1972 Appl. No.: 277,044

Foreign Application Priority Data Apr. 14, 1972 Japan 47-38172 U.S. C129/25.l2, 313/136, 313/141 Int. Cl. F23q 3/70, 1-10lt 13/00 1 Field ofSearch 29/25.l2, 520; 313/136, 313/141, 144

References Cited UNITED STATES PATENTS 10/1960 Beesch 313/141 3,144,5768/1964 Hagmaier 313/141 3,548,472 12/ 1970 Urushiwara et a1 3 l 3/ 136 XFOREIGN PATENTS OR APPLICATIONS 838,682 6/1960 Great Britain 29/25.12

Primary ExaminerRoy Lake Assistant Examiner-James W. Davie Attorney,Agent, or Firm-Cushman, Darby & Cushman [5 7 ABSTRACT 5 Claims, 12Drawing Figures PATENTEB [JEEB 1 I974 FIG 2 @w m F b BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to amethod for the production of a spark plug center electrode of the typein which the core member consisting of a good heat conducting metal suchas copper is inserted into the central part of the covering memberconsisting of a corrosion-resistant metal such as nickel.

2. Description of the Prior Art Methods of producing spark plug centerelectrodes are known in the art in which the covering member is formedby boring out a rod of corrosion-resistant metal such as nickel and thecore member consisting of a good heat conducting metal such as copper isthen inserted into the bore of the covering member and soldered thereto,or alternatively two cylindrical metal pieces of corrosion-resistantmetal and good heat conducting metal, respectively, are put one uponanother so that when they are extruded and shaped into a rod form in acold extrusion die, the core member of good heat conducting metal iscovered by the covering member of corrosion-resistant metal by virtue ofthe flowing effect of the metal. A disadvantage of the former method isthat the bore of the corrosion-resistant metal covering member forreceiving the core member made of good heat conducting metal is formedby a cutting process and thus this method is not satisfactory from thestandpoint of mass production efficiency. The latter method is alsodisadvantageous in that since the center electrode is made using twocylindrical metal pieces, as shown in FIG. 1, there is a limit to thelength a of the corrosion-resistant metal covering member 2b coveringthe core member and moreover the covering member 2b increases toward itsend at the sparking side and decreases toward the opposite end in itsthickness b thereby making it impossible to ensure a uniform heatradiation.

SUMMARY OF THE INVENTION It is the object of the present invention tosolve these difficulties. In accordance with the present inventiontherefore, there is provided a method of producing a spark plug centerelectrode which comprises a first step of forming a metal piece of goodheat conductivity into a convex shape and a corrosion-resistant metalpiece into a concave shape, a second step of preparing an extrusionmaterial by fitting the protruding portion of the convex-shaped goodheat conducting metal piece into the recessed portion of theconcave-shaped corrosionresistant metal piece, a third step ofcold-extruding the extrusion material into a rod form with thecorrosionresistant metal covering the good heat conducting metal, afourth step of cutting the cold extruded material at that portionthereof where the corrosion resistant metal no longer covers the goodheat conducting metal, and a fifth step of subjecting the centerelectrode composed of the core member consisting of the good heatconducting metal and the corrosion-resistant metal covering member to aheading operation to form thereon a collar for assembling it into aspark plug, whereby the length of coverage of the corrosionresistantmetal covering member can be selected as desired with its thicknessbeing relatively uniform, and the core member can be covered with thecovering member without any cutting operation thus making the presentmethod well suited for mass production.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectional viewof a center electrode produced according to a conventional method ofproducing a spark plug center electrode.

FIG. 2 is a longitudinal sectional view of a good heat conducting metalpiece employed in the method for the production of a spark plug centerelectrode according to the present invention.

FIG. 3 is a longitudinal sectional view of a corrosionresistant metalpiece employed in the method for the production of a spark plug centerelectrode according to the present invention.

FIG. 4 is a longitudinal sectional view of an extrusion materialprepared by assembling the good heat conducting metal piece of FIG. 2and the corrosionresistant metal piece of FIG. 3.

FIG. 5 is a partial longitudinal sectional view of a cold extrusion diein which the extrusion material of FIG. 4 is placed.

FIG. 6 is a longitudinal sectional view of a center electrode with ahead, which is produced by the cold extrusion die of FIG. 5.

FIG. 7 is a longitudinal sectional view of the center electrode of FIG.6 with its head cut off.

FIG. 8 is a longitudinal sectional view showing a first embodiment ofthe center electrode of the invention produced by subjecting the centerelectrode of FIG. 7 to a heading operation to form a collar thereon.

FIG. 9 is a side view of the center electrode shown in FIG. 8.

FIG. 10 is a longitudinal sectional view showing a second embodiment ofthe center electrode of the invention produced by subjecting the centerelectrode of FIG. 7 to a heading operation to form a collar thereon.

FIG. 11 is a longitudinal sectional view of the center electrode of FIG.10 subjected to an expanding operation.

FIG. 12 is a side view of the center electrode shown in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will nowbe explained with reference to a first embodiment shown in theaccompanying drawings. According to this first embodiment, the firststep consists of plastic-working a metal piece I of good heatconductivity such as copper into a convex shape having a protrudingportion In as shown in FIG. 2 and a metal piece 2 of corrosion-resistantmaterial such as nickel into a concave shape having a recessed portion2a as shown in FIG. 3. In the second step, the good heat conductingmetal piece] and the corrosionresistant metal piece 2 worked plasticallyin the first step are assembled in such a manner that the protrudingportion la of the former is fitted into the recessed portion 2a of thelatter to produce an extrusion material 3. The two metal pieces 1 and 2can be bonded together, if required, by means of soldering, welding,thermal diffusion, pressure fitting and caulking, etc., so that theresultant extrusion material 3 may be conveniently placed in a coldextrusion die in a subsequent step. In the third step, the extrusionmaterial 3 prepared in the second step is placed in a cold extrusion die4 and it is then shaped into a rod form in cold extrusion under thepressure applied by a punch 5, producing a cold extruded productcomprising a covering member 2b consisting of the cup-shapedcorrosionresistant metal piece 2 and a core member 1b consisting of thegood heat conducting metal piece 1 covered by the covering member 2b. Acenter electrode 6 is thus obtained in which, as shown in FIG. 6, thecovering member 2b consisting of the corrosion-resistant metal 2 isuniform in its thickness b and its length a covering the core member lbis also long. In the fourth step, the center electrode 6 extruded asshown in FIG. 6 by the cold extrusion die is cut at that portion thereofwhere the corrosion-resistant metal of the center electrode 6 no longercovers the good heat conducting metal, i.e., at a dotted line X by meansof a lathe or the like, cutting off a head portion 7 of the centerelectrode 6 and thus shaping it into a form shown in FIG. 7. The fifthand final step consists of subjecting the center electrode 6 to aheading operation to form thereon a collar portion 8 as shown in FIGS. 8and 9 which is necessary for assembling the center electrode 6 into aspark plug.

In this heading operation, the center electrode 8 is worked to have apoint angle a at its end face and it is also worked by a punch havingits end face formed with radial V-grooves.

In accordance with a second embodiment of the present invention, in theheading operation the collar portion 8 may be formed on the centerelectrode 6 at a place slightly below its end face as shown in FIG. 10and thereafter the end face may be subjected to an expanding operationby the aforesaid punch as shown in FIG. 11 or 12.

It will thus be seen that since the method according to the presentinvention comprises the first step of forming a good heat conductingmetal piece into a convex shape and a corrosion-resistant metal pieceinto a concave shape, the second step of preparing an extrusion materialby fitting the protruding portion of the convex-shaped good heatconducting metal piece into the recessed portion of the concave-shapedcorrosionresistant metal piece, the third step of shaping the extrusionmaterial into a rod form by the process of cold extruding, the fourthstep of cutting off the thus coldextruded product at that portionthereof where the corrosion-resistant metal no longer covers the goodheat conducting metal, and the fifth step of subjecting the resultantcenter electrode comprising the core member made of the good heatconducting metal and the covering member made of the corrosion-resistantmetal to a heading operation to form thereon a collar portion forassemblying the center electrode into a spark plug, there is aremarkable effect in that the dimensions of the protruding portion ofthe good heat conducting metal piece and the recessed portion of thecorrosionresistant metal piece can be chosen as desired and that thethickness of the covering member consisting of the corrosion-resistantmetal below the mounting collar portion of the center electrode can alsobe selected as desired and made relatively uniform and more specificallythe thickness of the covering member on the end face at the sparkingside can also be adjusted as desired. There is another remarkable effectin that by subjecting the center electrode to a heading operation, asufficient amount of the good heat conducting metal of the centerelectrode can be exposed, thereby ensuring an adequate transmission ofheat to the glass sealing material and also a sufficient mechanicalsustaining strength. There is a further remarkable effect in that withthe use of a heading punch which is required to operate in the verticaldirection only, the operating method of the punch can be extremelysimplified thus permitting the production of center electrodes withinexpensive equipment. There is a still further remarkable effect inthat the core member can be covered with the covering member without anycutting operation, thereby ensuring an improved mass productionefficiency.

We claim:

1. A method of producing a spark plug center electrode of the type whichcomprises a core member consisting of a good heat conducting metalhaving a corrosion-resistant metal enclosing the sparking end portionand the side portions thereof, said method comprising the steps of:

forming said good heat conducting metal into a protrudent shape by onlyone plastic-working step, the protrudent portion of the shaped good heatconducting metal being at least as great as one-half the height of saidshaped good heat conducting metal,

forming a corrosion-resistant metal piece into a cup shape by only oneplastic working step, the depth of the cavity of said cup-shaped metalbeing at least as great as one-half the height of said cup-shaped metal,preparing an extrusion metal by fitting the protruding portion of saidprotrudent shaped good heat conducting metal piece into the recessportion of said cup-shaped corrosion resistant metal piece, and

shaping said extrusion metal into a rod formed by the process of coldextrusion, wherein said good heat conducting metal is covered by saidcorrosion resistant metal.

2. A method according to claim 1 including a further step of cuttingsaid cold-extruded product at that portion thereof where the length ofsaid corrosion-resistant metal covering said good heat conducting metalterminates.

3. A method according to claim 2 including a further step of subjectingthe center electrode comprising the core member consisting of said goodheat conducting metal and the covering member covering said core memberand consisting of said corrosion-resistant metal to a heading operationto form thereon a collar portion for assemblying said center electrodeinto a spark plug.

4. A method according to claim 3, wherein said good heat conductingmetal consists of copper and said corrosion-resistant metal consists ofnickel.

5. A method of producing a spark plug center electrode of the type whichcomprises a core member consisting of a good heat conducting metalhaving a corrosion-resistant metal enclosing the sparking end portionand the side portions thereof, said method comprising the steps of:

forming said good heat conducting metal into a protrudent shape by onlyone plastic-working step wherein the protruding portion of said goodheat conducting metal is at least as great as one-half the length of theshaped good heat conducting metal,

ducting metal piece into the cavity portion of said complementary-shapedcorrosion-resistant metal piece, and

shaping said extrusion metal into a rod formed by the process of coldextrusion, wherein said good heat conducting metal is substantiallyuniformly covered by said corrosion-resistant metal.

1. A method of producing a spark plug center electrode of the type whichcomprises a core member consisting of a good heat conducting metalhaving a corrosion-resistant metal enclosing the sparking end portionand the side portions thereof, said method comprising the steps of:Forming said good heat conducting metal into a protrudent shape by onlyone plastic-working step, the protrudent portion of the shaped good heatconducting metal being at least as great as one-half the height of saidshaped good heat conducting metal, forming a corrosion-resistant metalpiece into a cup shape by only one plastic working step, the depth ofthe cavity of said cup-shaped metal being at least as great as one-halfthe height of said cup-shaped metal, preparing an extrusion metal byfitting the protruding portion of said protrudent shaped good heatconducting metal piece into the recess portion of said cup-shapedcorrosion resistant metal piece, and shaping said extrusion metal into arod formed by the process of cold extrusion, wherein said good heatconducting metal is covered by said corrosion resistant metal.
 2. Amethod according to claim 1 including a further step of cutting saidcold-extruded product at that portion thereof where the length of saidcorrosion-resistant metal covering said good heat conducting metalterminates.
 3. A method according to claim 2 including a further step ofsubjecting the center electrode comprising the core member consisting ofsaid good heat conducting metal and the covering member covering saidcore member and consisting of said corrosion-resistant metal to aheading operation to form thereon a collar portion for assemblying saidcenter electrode into a spark plug.
 4. A method according to claim 3,wherein said good heat conducting metal consists of copper and saidcorrosion-resistant metal consists of nickel.
 5. A method of producing aspark plug center electrode of the type which comprises a core memberconsisting of a good heat conducting metal having a corrosion-resistantmetal enclosing the sparking end portion and the side portions thereof,said method comprising the steps of: forming said good heat conductingmetal into a protrudent shape by only one plastic-working step whereinthe protruding portion of said good heat conducting metal is at least asgreat as one-half the length of the shaped good heat conducting metal,forming a corrosion-resistant metal piece into a complementary shapehaving a cavity therein for receiving said protruding portion of saidgood heat conducting metal, the depth of said cavity being at least asgreat as one-half the height of said complementary-shaped metal piece,preparing an extrusion metal by fitting the protruding portion of saidprotrudent-shaped good heat conducting metal piece into the cavityportion of said complementary-shaped corrosion-resistant metal piece,and shaping said extrusion metal into a rod formed by the process ofcold extrusion, wherein said good heat conducting metal is substantiallyuniformly covered by said corrosion-resistant metal.